be2net: Fix buffer overflow in be_get_module_eeprom

be_cmd_read_port_transceiver_data assumes that it is given a buffer that
is at least PAGE_DATA_LEN long, or twice that if the module supports SFF
8472. However, this is not always the case.

Fix this by passing the desired offset and length to
be_cmd_read_port_transceiver_data so that we only copy the bytes once.

Fixes: e36edd9d

 ("be2net: add ethtool "-m" option support")
Signed-off-by: Hristo Venev <hristo@venev.name>
Link: https://lore.kernel.org/r/20220716085134.6095-1-hristo@venev.name
Signed-off-by: Paolo Abeni <pabeni@redhat.com>